Calculating the Perimeter for a polygon shapefile

1. Optionally, start an edit session in ArcMap. Calculating a field is faster outside of an edit session, but you won't be able to undo the calculation.
2. Open the attribute table of the layer you want to edit.
3. Right-click the field heading for perimeter (if there is no field holding perimeter values you can add a new field for perimeter by clicking the options button and selecting the new field option).
4. Click Calculate Values.
5. Check Advanced.
6. Type the following VBA statement in the first text box:

Dim dblPerimeter as double
Dim pCurve as ICurve
Set pCurve = [shape]
dblPerimeter = pCurve.Length

7. Type the variable dblPerimeter in the text box directly under the perimeter field name.
8. Click OK.

Tip: The property length returns a field type of double. For best results, your length field should also be a double field type.

This text comes directly from the ArcGIS help window and can be reached by first locating "Fields in tables" in the index and then "calculating values".

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